We prepare our gardens for dormancy and ready ourselves for the long winter season with the annual ritual of cutting back. But how we do so significantly affects the survival of many garden plants in our harsh Chicago climate.
FOR MOST PLANTS,
don’t prune in late summer or cut back too early in the fall. Some woody plants like roses are encouraged to put out new growth if they are pruned in August or September, which saps the plant’s
strength. Other plants are going through
a long physiological process that helps them
survive very cold temperatures. This preparation
for dormancy is interrupted by cleaning up
too early. So, cut back most perennials any
time from November to April. And you may
find that many plants have interesting and
beautiful winter appearance. Try leaving
dead perennial foliage and seeds standing
for a while to see if you find them attractive
in your winter garden.
Take care of these EXCEPTIONS
earlier in fall: plants which are susceptible
to powdery mildew, botrytis and other fungal
diseases. Their dead foliage may harbor the
spores that allow the disease to over-winter
and re-infect your plants the following year.
Cut the plants back before leaf drop: peony,
garden phlox, iris and bee balm and (don’t cut back but) remove fallen rose foliage to reduce next year’s infestation of black spot. Remove the foliage entirely from your property—don’t
even add it to your compost pile or you may
just reintroduce the spores next year.
MORE EXCEPTIONS: These
plants benefit by not being cut back until
new growth starts in spring. We grow these
as perennials but they are actually more
like shrubs which sprout new growth from
their stems rather than from their roots.
If we cut them to the ground, and in fall,
as we do some of the perennials, they will
come back weakly or not at all. The prime
example is lavender—don’t cut back until new growth starts in spring and then be sure to leave many new buds on the lower stems. In the spring, prune the following back to a point above where you see new growth (about 6” above
the soil): butterfly bush (Buddleia), Russian
sage, blue mist shrub (Caryopteris).
We don’t exactly know why, but these plants survive the winter better if not cut back until spring: Frikart’s aster (Aster
frikartii `Monch’), garden mums, Fallopia, bush clover (Lespedeza), shasta daisy—particularly `Becky’ (`Ryan’s White’),
red cardinal flower and lungwort. They may
require even more time for physiological
preparation for winter, or the dead foliage
may act as mulch, protecting the delicate
crown.
And finally, keep some plants through the winter to benefit from their special contribution to the winter landscape. Many ornamental grasses make their best contribution to the landscape in winter, when most other herbaceous plants have disappeared. Add to these the evergreen and semi-evergreen perennials such as Lenten rose and other Hellebores, barrenwort (Epimedium) and herbs such as thyme and sage. For a detailed, plant-by-plant examination of dividing and other care, I suggest a great book, The Well-Tended Perennial Garden by Tracy DiSabato-Aust.
© Andrea Green 2006
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